Scala : sandbox: Scala : add 7-variance

1 files changed, 25 insertions, 0 deletions

diff --git a/Scala/sandbox/7-variance.scala b/Scala/sandbox/7-variance.scala
new file mode 100644
index 0000000..49f0373
--- /dev/null
+++ b/Scala/sandbox/7-variance.scala
@@ -0,0 +1,25 @@
+object Variance
+{
+  // to allow 
+  trait List[+T] {
+    def isEmpty: Boolean
+    def head: T
+    def tail: List[T]
+  }
+
+  class Cons[T](val head: T, val tail: List[T]) extends List[T] {
+    def isEmpty = false
+  }
+
+  // extends List[Nothing] so that it can hold anything
+  object Nil extends List[Nothing] {
+    def isEmpty = true
+    def head: Nothing = throw new NoSuchElementException("Nil.head")
+    def tail: Nothing = throw new NoSuchElementException("Nil.tail")
+  }
+
+  def run = {
+    println("Variance")
+    val x: List[String] = Nil
+  }
+}